Underground metallic ducts lacking an approved coating must be encased in how many inches of concrete?

• A. 3
• B. 2
• C. 4
• D. 5

Answer: (B)

Underground metallic ducts that don’t have an approved coating are at risk from moisture, soil chemicals, and physical damage. To protect them, a concrete encasement is used, which acts as a barrier and helps distribute loads from backfill and surface pressure. The required thickness for this protection is two inches of concrete. If the duct has an approved coating, that coating provides corrosion protection, so the encasement requirement can vary, but for uncoated ducts, two inches is the standard minimum.